The present invention relates to an idle speed control apparatus for controlling the idle speed of an internal combustion engine used as a prime mover for driving an automobile. More particularly, the invention relates to an idle speed control apparatus for automatically adjusting the idle speed of an internal combustion engine in accordance with the operating condition of the refrigerant compressor of a vehicle compartment air conditioner which is a load unit of the engine.
In the past, a typical vehicle compartment air conditioner has included a refrigerant compressor adapted to be coupled and uncoupled through a magnetic clutch thereby controlling the cooling of air in an on-off manner. This on-off type air cooling is disadvantageous in that the supply air temperature varies considerably and the load on the engine varies greatly. A variable capacity type compressor has the advantage of adjusting the refrigerant delivery capacity per unit time continuously or in a stepwise manner and thereby ensuring the required cooling effect and also reducing the variations of the power load.
The control system of the variable capacity type compressor varies the delivery capacity in accordance with the heat load conditions including the temperatures inside and outside the vehicle compartment and the amount of solar radiation and/or the cooling condition of the cooling heat exchanger (the evaporator) and therefore the load on the engine forming a driving source frequently varies from moment to moment irrespective of the operating conditions of the engine. In this case, to cause the idle speed of the engine to faithfully follow the magnitude of the load is important from the standpoint of preventing such irregularity as speed variation in the engine and also from the standpoint of reducing the fuel consumption to the minimum required value.